Concept Presentation Limiting Reactants
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Transcript of Concept Presentation Limiting Reactants
Namrta Bhardwaj
Background Information
Prerequisite knowledge should include nomenclature balancing chemical equations. Mole to mole and mass to mole calculation
It is important that students understand the law of conservation of mass
Students should also be skilled in using ratios and conversion factors in calculations.
Curriculum Expectations
Overall expectations:D2. Investigate quantitative relationships in
chemical reactions, and solve related problems
D3. Demonstrate an understanding of the mole concept and its significance to the quantitative analysis of chemical reactions
Specific expectationsD2.1 Use appropriate terminology related to quantities in
chemical reactions, including, but not limited to: stoichiometry, percentage yield, limiting reagent, mole, and atomic mass [C]
D2.5 Calculate the corresponding mass, or quantity in moles or molecules, for any given reactant or product in a balanced chemical equation as well as for any other reactant or product in the chemical reaction [AI]
D2.6 Solve problems related to quantities in chemical reactions by performing calculations involving percentage yield and limiting reagents [AI]
D3.4 Explain the quantitative relationships expressed in a balanced chemical equation, using appropriate units of measure (e.g., moles, grams, atoms, ions, molecules)
Place in the Curriculum
Placement Within the Unit Counting Atoms and Molecules: The Mole
The Avogadro Constant and the Mole Molar Mass
Chemical Proportions in Compounds Percentage Composition Empirical Formula of a Compound Molecular Formula of a Compound
Quantities in Chemical Reactions Stoichiometry Limiting Reactant Percentage Yield
Misconceptions / Learning Difficulties
When the mass of both reactants is given students have difficulty recognizing that one of the masses is limiting and the other mass is in excess.
randomly select one of the given masses as limiting or excess
assume that the masses are in the correct mole ratios students
assume the smaller mass is the limiting reagent.
Need to point out these are not trick questions Important to stress the common steps in converting
masses into amounts in moles in order to relate to mole ratios in balanced equations.
Demonstrate ReactionWhich reactant is limiting and which is in
excess reactant?
Use copper chloride reacting with Aluminum to illustrate a mass to mole relationship
Container Al:CuCl2 Ratio
Mass of Al Foil/g
A Control 0.00B 1:1 mass
ratio2.06
C 1:1 mole ratio
2.06
D 2:3 mass ratio
1.37
E 2:3 mole ratio
0.27
MisconceptionsIf reactants are in the same physical state the
reaction reaches completion when both reactants are totally converted
Or
If the reactants are in two different physical states (solid and liquid) the reaction reaches completion when the entire solid is consumed.
Reaction of Mg with HCl
MisconceptionsStudents have limited view of chemical
system since they have been taught to consider a reaction system as: reactants -> products
rewrite equation as: Reactants -> Products + excess reactant
Gizmo Activity
Gizmo Activity
Gizmo Activity
Supporting Diverse Student NeedsChallenge gifted students -How many grams of a
particular starting material will remain at the end of a reaction?
Encourage gifted students to develop their own methods for solving problems - do not follow given format
ELL students have difficulty understanding verbal explanations - may benefit from writing out the thought process used in solving sample problems.
Students that required more support may be given more scaffolding and support in questions.
Have students make common sense prediction when solving problems.
Lesson Sequence Teaching Strategies Learning Styles (MI) Assessment
Take up homework , Review mass to mass calculation
Use hot dogs and hot dog bun analogy to introduce concept of limiting reactants
Demo- Na – Water rxn
Have students provide alternative analogies
Copper chloride and Aluminum lab
Teacher directed – student participate
Discussion
Demo
Think-pair-share
Demo
Visual, Auditory(Logical/ Mathematical)
Auditory(Verbal/ Linguistic, Logical/ Mathematical)
Visual, Auditory (visual/ spatial)
Auditory (Verbal/ Linguistic, Intrapersonal, Interpersonal)
Visual, Auditory (visual/ spatial, Logical/ Mathematical)
For learningHomework check, assess student’s answers as homework is being taken up
Lesson Sequence Teaching Strategies Learning Styles (MI) AssessmentHave students brainstorm practical reasons for having limiting reactants
Have students conduct baking soda and vinegar lab (or Mg and HCl) lab
Discussion
Guided inquiry
Auditory(Verbal/ Linguistic)
Kinesthetic (kinesthetic, visual/spatial)
Exit pass: For the reaction of copper chloride and aluminum which of the statements is true and explain why: Equal masses of reactants will react completely in a chemical equation. Chemicals react based on mole ratios found in a chemical equation. Chemicals react based on mass ratios found in a chemical equation. Equal moles of reactants will react completely in a chemical reaction.
Lesson Sequence Teaching Strategies
Learning Styles (MI) Assessment
Solve sample problems
Provide students with a flow chart to follow
Start with balanced chemical reactions that has reactants in a 1:1 mole ratio
Progress to more difficult sample problems
Direct instruction Visual, Auditory(visual/ spatial, logical/ mathematical)
For learning 3...2...13 things I know about stoichiometry.....2 things I am getting better at......1 thing I still need help with......
Lesson Sequence Teaching Strategies Learning Styles (MI) Assessment
Day 3Extra practiceHave groups display answers on white boards – gallery walk
Cooperative grouping
Visual, Auditory(visual /spatial, Logical/ Mathematical)
As learning and for learningAssess student’s cooperative skills, participation skills and answers to questions
Day 4Quiz on limiting and excess reactantsPercent Yield Calculations
Direct Instruction Visual, Auditory(Logical/ Mathematical)
Of learning – mark quiz
Day 5Conduct Limiting and excess lab with percent yield calculation
Guided inquiry Visual, Kinesthetic (visual / spatial, kinesthetic)
Of learning- collect and mark lab
Applications and Societal Implications
Careers in Chemistry – Chemical EngineerCooking recipes, industrial reactions, prescription
drug dosages, manufacturing, building (constructions)
The amount of carbon on earth is the ultimate limiting reagent for the number of people the earth can have and in the sense that carbon is our "food"... the land area of the earth is a "limiting reagent" that will limit our population before carbon does.... L. H. Holmes Jr.
Advanced PreparationDay 1Refer to Interactive Demonstrations for Mole Ratios
and Limiting Reagents (annotated reference 1) and prepare material for the lab accordingly.
Refer to How Big Is the Balloon? Stoichiometry Using Baking Soda and Vinegar (annotated reference 6) and prepare material for the lab accordingly.
Day 5Refer to pg 165 of the Nelson teacher’s resource for
percentage yield in a chemical reaction lab and prepare material for the lab accordingly.
Safety ConsiderationsRemember to always wear safety goggles. Reaction of Na with water demoNever use a piece of sodium larger than a ½ pea
r. The reaction should be carried out behind a clear
safety barrier or at a distance from the students Reaction of Copper (II) chloride with AluminumCopper(II) chloride is toxic by ingestion and
irritating to skinAluminum will also react with the solution to
produce hydrogen gas. Flames should not be used in this investigation
Reaction of baking soda with vinegarAvoid getting baking soda or vinegar in eyes
Annotated ReferencesBreyfogle, Bryan. (2006) Interactive Demonstrations for Mole Ratios and Limiting Reagents. Journal of Chemical Education,
85 (5), 741.The demonstration of the mole and mass ratios for the reaction of CuCl2 and Al were obtained from this article. Clyde, Dillard R. (1972) Two Lecture Experiments Demonstrating Limiting Quantities. Journal of Chemical Education, 49
(12), A694.Resource used for conducting limiting reactant experiment using Mg and HCl. Gauchon, Laure, et al. (2007) Learning About Stoichiometry: From Students’ Preconceptions to the Concept of Limiting
Reactant . Chemistry Education Research and Practice, 8 (4), 362-375.Article discusses many misconceptions that student encounter with studying limiting reactants. Holmes, L. H. Jr. (1998) Limiting Reagent and Kinetics: Social Implications and Malthus' Prediction. Journal of Chemical
Education, 75 (8), 1004.Interesting article that discusses food supply and land area in terms of limiting reagents. Jenkins, Frank, et al. (2002). Chemistry 11. Toronto: Nelson. (course textbook) Journal’s Editorial Staff (1997). How Big Is the Balloon? Stoichiometry Using Baking Soda and Vinegar. Journal of Chemical
Education, 74 (2), 1328A-1328B.Article used for the Baking soda and vinegar lab. Resource used for conducting limiting reactant experiment using vinegar and baking soda.Kalanter, A.H. (1985) Limiting Reagent Problems Made Simple for Students. Journal of Chemical Education, 62 (2), 106.Article used to for the ICE method for solving limiting reactants. Mustoe, Frank, et al. (2201). Chemistry 11. Toronto: McGraw-Hill Ryerson. (course textbook)
Annotated ReferencesWebsites:http://www.chalkbored.com/lessons/chemistry-11.htmgood power point presentation on limiting/ excess
reactants, also the chart method for solving limiting reactant problems was taken from this site
http://www.youtube.com/watch?v=xk7PSpFC7NI&feature=relateddemonstration of the flaming table and whoosh
bottle http://www.chemprofessor.com/flow chart method was obtained from this site